Direct I/O access to express bussing in a configurable logic array

ABSTRACT

The present invention provides a configurable logic array that includes a plurality of individually configurable logic cells arranged in a generally rectangular matrix that includes a plurality of horizontal rows of logic cells and a plurality of vertical rows of logic cells. The array further includes at least one horizontally aligned express bus running between adjacent rows of logic cells, the logic cells in the adjacent rows being connectable thereto, and at least one vertically aligned express bus running between adjacent columns of logic cells, the logic cells in the adjacent columns being connectable thereto. The array further includes a plurality of logic cell I/O pins located at the periphery of the matrix and connectable to the logic cells in the rows and columns at the periphery of the matrix. Furthermore, the array includes a plurality of express bus I/O pins directly connectable to the express busses.

This is a continuation of co-pending application Ser. No. 08/015,466filed on Feb. 8, 1993, now abandoned, which is a divisional ofapplication Ser. No. 07/752,282 filed on Aug. 29, 1991, now abandoned.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is related to U.S. patent application Ser. No.752,414, filed on Aug. 30, 1991 by Furtek and Camarota for PROGRAMMABLELOGIC CELL AND ARRAY, which is a continuation-in-part of U.S. patentapplication Ser. No. 07/608,415, filed on Nov. 2, 1990.

Both of the above-cited related applications are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to user programmable integratedcircuit devices and, in particular, to the provision of a plurality ofexpress bus I/O pins directly connectable to the express buses in aconfigurable logic array.

2. Discussion of the Prior Art

A configurable logic array (CLA) is a matrix of interconnected,programmable logic cells. The individual logic function and the activeinputs and outputs of each logic cell are determined by parameterflip-flops and logic gates within the cell, rather than by physicallycustomizing the array during manufacture. Thus, the individual cellfunctions and the interconnections between cells are dynamicallyprogrammable to provide a wide variety of functions. The greater thenumber of cells in the array, the greater the functional flexibility ofthe CLA device.

The configurable logic array concept was first introduced by Sven E.Wahlstrom in 1967. Wahlstrom, Electronics, Dec. 11, 1967, pp. 90-95.

Since then, Xilinx Inc., Actel Inc., Pilkington Micro-electronics Ltd.and Concurrent Logic, Inc., among others, have proposed implementationsof CLA devices.

The basic Xilinx CLA architecture is disclosed in U.S. Pat. No.4,870,302, which issued to Ross H. Freeman on Feb. 19, 1988.

The CLA device described by the Xilinx '302 patent and shown in FIG. 1includes an array of configurable logic elements that are variablyinterconnected in response to control signals to perform selectedoverall logic functions. Each configurable element in the array iscapable of performing a number of logic functions depending upon thecontrol information provided to that element. The array can have itsfunctions varied at any time by changing its control information.

FIG. 2 shows a CLA interconnected structure currently utilized in theXilinx array. In addition to the single-length interconnect linesbetween logic elements, as shown in FIG. 2, the Xilinx array utilizeslines that connect switch matrices, e.g., two vertical and twohorizontal double-length lines per logic-element column. The Xilinxarray also utilizes "global" interconnect lines, e.g., six verticalglobal lines and six horizontal global lines per logic-element column,for clocks, resets and other global signals. Two of the horizontalglobal lines are may be placed in a high impedance state.

FIG. 3 shows a logic-element currently utilized in the Xilinx array. TheXilinx logic element has three function generators, two flip-flops, andseveral multiplexers. The first two function generators can perform aBoolean function of four inputs. The function generators are implementedas memory look-up tables. The outputs of these two function generatorsare provided to the multiplexers and to a three-input function generatorwhich can perform a Boolean function of G', F', and an external input.The output of the third function generator is also provided to themultiplexers. The multiplexers select whether the signals are providedto the output of the logic element or to the input of the flip-flops.The flip-flops have common clock, enable, and set or reset inputs. Theconfiguration bits that determine the function of the logic element alsodetermine how the C1 through C4 inputs are mapped into the four inputsH1, DIN, S/R, and EC.

The basic Pilkington CLA architecture is disclosed in U.S. Pat. No.4,935,734, which issued to Kenneth Austin on Sep. 10, 1986.

An implementation of the CLA architecture disclosed in the Pilkingon'734 patent is shown in FIG. 4. Each logic element in the array acceptsinputs from four other logic elements in the illustrated pattern. Eachlogic element output drives multiple other elements as illustrated. Inthe array disclosed in the '734 patent, there is no additional wiring.However, the Plessey Company, under license from Pilkington, hasmarketed a product wherein bus wiring is added as shown in FIG. 4; i.e.in every third column, a bus provides inputs to every right-directionlogic element in that columns, and every third row has a bus providinginputs to every left-direction logic element in that row.

FIG. 5 shows a logic cell currently utilized in the FIG. 4 array. Asshown in FIG. 5, each of the two inputs to a NAND gate are provided by auser configured multiplexer the inputs of which are provided by otherlogic elements or inputs. Plessey has also added circuitry to the logicelement to permit it to be a latch or a 2-input NAND gate.

The basic Actel CLA architecture is disclosed in U.S. Pat. No.4,873,459, issued to El Gamal et al. on Oct. 10, 1989.

The Actel architecture relies on one-time programmable anti-fuses forconfigurability and, thus, is not re-programmable.

The Concurrent Logic, Inc. (CLI) CLA architecture, which is mostrelevant to the present invention, is discussed below in conjunctionwith FIGS. 6-17. Features of the CLI CLA architecture are disclosed inthe following U.S. Patents issued to Frederick C. Furtek: U.S. Pat. Nos.4,700,187, issued Oct. 13, 1987; 4,918,440, issued Apr. 17, 1990; and5,019,736, issued May 28, 1991.

As discussed in above-cited related application Ser. No. 07/608,415, aCLA may be viewed as an array of programmable logic on which a flexiblebussing network is superimposed. As shown in FIG. 6, the heart of theCLI CLA 10 is a two-dimensional array of logic cells 12 each of whichreceives inputs from and provides outputs to its four adjacentneighbors. The core logic cell 12, which is shown in detail in FIG. 7,can be programmed to provide all the wiring and logic functions neededto create any digital circuit.

Each logic cell 12 in the array, other than those on the periphery,receives eight inputs from and provides eight outputs to its North (N),East (E), South (S), and West (W) neighbors. These sixteen inputs andoutputs are divided into two types, "A" and "B", with an A input, an Aoutput, a B input and a B output for each neighboring cell 12. Betweencells 12, an A output is always connected to an A input and a B outputis always connected to a B input.

As further shown in FIG. 7, within a cell 12, the four A inputs enter auser-configurable multiplexer 14, while the four B inputs enter a seconduser-configurable multiplexer 16. The two multiplexer outputs feed thelogic components of the cell 12. In logic cell 12, these componentsinclude a NAND gate 18, a register 20, an XOR gate 22, and twoadditional user-configurable multiplexers 24 and 26.

The two four-input multiplexers 24 and 26 are controlled in tandem(unlike the input multiplexers), giving rise to four possible logicconfigurations, shown in FIGS. 8A-8D.

In the FIG. 8A configuration, corresponding to the "0" inputs of themultiplexers 24 and 26, the A outputs are connected to a single A inputand the B outputs are connected to a single B input.

In the FIG. 8B configuration, corresponding to the "1" inputs of themultiplexers 24 and 26, the A outputs are connected to a single B inputand the B outputs are connected to a single A input.

In the FIG. 8C configuration, corresponding to the "2" inputs of themultiplexers 24 and 26, the A outputs provide the NAND and the B outputsthe XOR of a single A input and a single B input. This is the equivalentof a half adder circuit.

In the FIG. 8D configuration, corresponding to the "3" inputs of themultiplexers 24 and 26, the Q output of edge-triggered D flip-flop 20 isconnected to the A outputs, the D input of the flip-flop 20 is connectedto a single A input, the enable (EN) input of the flip-flop 20 isconnected to a single B input and the B outputs provide the logicalconstant "1". A global clock input and register reset are provided forthis configuration, but are not illustrated in FIG. 8D. Thisconfiguration is equivalent to a one bit register.

The cell 12 thus provides the most fundamental routing and logicfunctions: extensive routing capabilities, NAND and XOR (half adder), aone-bit register, the logical constant "1", and fan-out capabilities.

These functions permit the basic CLA array 10 to implement arbitrarydigital circuits. A register and half adder (NAND and XOR) included ineach cell 12, together with a high cell density, make the array 10 welladapted for both register-intensive and combinatorial applications. Inaddition, signals passing through a cell 12 are always regenerated,ensuring regular and predictable timing.

Although the basic logic array 10 is completely regular, routing wiresthrough individual cells 12 can cause increased delays over longdistances. To address this issue, the neighboring interconnect providedby the array 10 is augmented with three types of programmable busses:local, turning, and express.

Local busses provide connections between the array of cells and thebussing network. They also provide the wired-AND function.

Turning busses provide for 90° turns within the bussing network enablingT-intersections and corners. Turning busses provide faster connectionsthan do local busses, since they do not have the delays associated withusing a cell as a wire.

Express busses are designed purely for speed. They are the fastest wayto cover straight-line distances.

There is one bus of each type described above for each row and eachcolumn of logic cells 12 in the array 10. Connective units, callsrepeaters, are spaced every eight cells 12 and divide each bus intosegments spanning eight cells 12. Repeaters are aligned into rows andcolumns, thereby partitioning the basic array 10 into 8×8 blocks ofcells 12 called "superblocks". FIG. 9 illustrates a simplified view of abussing network containing four superblocks. Cell-to-cell connectionsare not shown.

As shown in FIG. 10, each local bus segment 13 is connected to eightconsecutive cells 12. As shown in FIG. 11, each turning bus segment 15is connected to eight orthogonal turning busses through programmableturn points. As shown in FIG. 12, each express bus segment 17 isconnected only to the repeaters at either end of the 8×8 superblock.FIG. 13 shows the three types of busses combined to form the bussingnetwork of the array 10.

In order for the bussing network to communicate with the array 10, eachcore logic cell 12 is augmented as shown in FIG. 14 to permit thereading and writing of local busses L. The cell 12 reads a horizontallocal bus through the "L_(X) " input of the B input multiplexer 16 andreads a vertical local bus through the "L_(Y) " input of the B inputmultiplexer 16. The cell 12 writes to a local bus through the driver 28connected to the A output.

While the cell 12 may read either a horizontal or a vertical bus underprogram control, the cell 12 may write to only one bus of fixedorientation. Whether a cell 12 writes to a horizontal or vertical bus isdetermined by its location with the array 10. Referring back to FIG. 10,the cell 12 in the upper-left corner of the illustrated superblockwrites to a horizontal local bus. If a particular cell 12 writes to ahorizontal local bus, then its four immediate neighbors write tovertical local busses, and vice versa.

As shown in FIG. 13, the two types of cells 12 are thus arranged in achecker-board pattern where the black cells 12 write to horizontalbusses and the white cells 12 write to vertical busses.

The CLA busses can be driven by the bus driver 28 in two ways. The busdriver 28 has two control bits, "TS" and "OC", which provide highimpedance and open-collector capabilities, respectively. The capability,which is independently programmable for each cell 12, allows the busdriver to be disconnected from the bus when the cell 12 is not beingused to write to the bus.

The open-collector capability provides the wired-AND function whenmultiple cells 12 are driving the same local bus simultaneously. Unlikethe high impedance function, which is controlled at the cell level, theopen-collector function is controlled at the bus level; all cells 12driving the same local bus are in the same open-collector state. Theprogramming environment insures that if there is exactly one driver 28driving a local bus, then that driver 28 provides active pull-up andactive pull-down. (The open-collector capability is turned off.) In allother cases, the drivers 28 driving a local bus provide passive pull-upand active pull-down. (The open-collector capability is turned on.)

In the special case when there are no drivers 28 driving a local bus(that is, when bus is not used), the open-collector capability is turnedon up resistor. An unused local bus, therefore, provides a logical "1"to those cells reading the bus.

As stated above, repeaters provide connections between busses. Eachrepeater is programmable so that any bus on one side of a repeater canbe connected to any bus on the other side of the repeater, as shown inFIG. 15. Each connection is unidirectional (direction is not depicted inFIG. 15) since repeaters always provide signal representation. Thedirection, like the connection itself, is programmable. Includingdirection, there are 18 (2×9) repeater configurations providing oneconnection, 72 (4×18) providing two connections, and 48 (8×6) providingthree connections.

As shown in FIG. 16, logic 19 for distributing clock signals to the Dflip-flops 20 in the logic cells 12 is located along one edge of thearray 10. The distribution network is organized by column and permitscolumns of cells 12 to be independently clocked. At the head of eachcolumn is a user-configurable multiplexer 30 providing the clock signalfor that column. There are four inputs to each multiplexer 30: anexternal clock supplied from off chip, the logical constant "0", theexpress bus adjacent to the distribution logic, and the A output of thecell 12 at the head of the corresponding column.

Through the global clock, the network provides low-skew distribution ofan externally supplied clock to any or all of the columns of the array10. The constant "0" is used to reduce power dissipation in columnscontaining no registers. The express bus is useful in distributing asecondary clock to multiple columns when the external clock line is usedas a primary clock. The A output of a cell is useful in providing aclock signal to a single column.

All D flip-flops 20 of the cells 12 of the array 10 may be globallyreset through an externally supplied signal entering the RESET controlpin.

The CLA array 10 provides a flexible interface between the logic array,configuration control logic and the I/O pads of the CLA device. As shownin FIG. 17, two adjacent cells, an "exit" cell 12a and an "entrance"cell 12b, on the perimeter of the logic array are associated with eachI/O pad 32. The A output of the exit cell 12a is connected, underprogram control, to an output buffer 34. The edge-facing A input of theadjacent entrance cell 12b is connected to an input buffer 36. Theoutput of the output buffer 34 and the input to the input buffer 36 areboth connected to the I/O pad 32. Control of the I/O logic is providedby various control signals and bits, as shown in FIG. 17.

While the CLA array 10 described above provides a wide range ofconfiguration options, it would be desirable to have available a CLAdevice that provide an even greater level of programmable flexibility.

SUMMARY OF THE INVENTION

A better understanding of the features and advantages of the presentinvention will be obtained by reference to the following detaileddescription and accompanying drawings which set forth an illustrativeembodiment in which the principles of the invention are utilized.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a portion of a first type ofconventional configurable logic array architecture.

FIG. 2 is a schematic diagram illustrating a cell-to-cell interconnectstructure utilizable in the FIG. 1 CLA array.

FIG. 3 is a is a logic diagram illustrating a logic cell utilizable inthe FIG. 1 CLA array.

FIG. 4 is a logic diagram illustrating a portion of a second type ofconventional configurable logic array architecture.

FIG. 5 is a logic diagram illustrating a logic cell utilizable in theFIG. 4 CLA array.

FIG. 6 is a block diagram illustrating a portion of third type ofconventional configurable logic array.

FIG. 7 is a logic diagram illustrating a logic cell utilizable in theFIG. 6 CLA array.

FIGS. 8A-8D are simple logic diagrams illustrating four possible logicconfigurations of the FIG. 7 logic cell.

FIG. 9 is a schematic diagram illustrating a bussing network for theFIG. 6 CLA array.

FIG. 10 is a schematic diagram illustrating local bus segments for theFIG. 9 bussing network.

FIG. 11 is a schematic diagram illustrating turning bus segments for theFIG. 9 bussing network.

FIG. 12 is a schematic diagram illustrating express bus segments for theFIG. 9 bussing network.

FIG. 13 is a schematic diagram illustrating the combination of thelocal, turning and express bus segments of the FIG. 9 bussing network.

FIG. 14 is a schematic diagram illustrating the FIG. 7 logic cellaugmented to permit read/write of local busses.

FIG. 15 illustrates the multiple possible repeater configurations forinter-bus connections in the FIG. 9 bussing network.

FIG. 16 is a block diagram illustrating clock distribution logicutilizable in the FIG. 6 CLA array.

FIG. 17 is a logic diagram illustrating "exit" and "entrance" cellsassociated with each I/O pad of the FIG. 6 CLA array.

FIG. 18 is a block diagram illustrating a portion of a configurablelogic array in accordance with the present invention.

FIG. 19 is a block diagram illustrating the bus turning capability of alogic cell of the FIG. 18 CLA array.

FIG. 20 is a schematic representation illustrating the interface betweena cell and local busses in the FIG. 18 CLA array.

FIG. 20A is a schematic representation illustrating an alternateinterface between a cell and the local busses of the FIG. 18 CLA array.

FIG. 21 is a schematic representation illustrating the implementation ofindividual control of the local busses in the FIG. 18 CLA array.

FIG. 22 is a block diagram illustrating express busses in the FIG. 18CLA array.

FIG. 23A is a schematic representation illustrating utilization ofrepeaters in the FIG. 18 CLA array.

FIG. 23B is a schematic representation illustrating repeaters utilizedin the FIG. 18 CLA array.

FIG. 24 is a schematic representation illustrating diagonal connectionsbetween abutting logic cells in the FIG. 18 CLA array.

FIG. 25 is a schematic representation illustrating diagonal local bussesin the FIG. 18 CLA array.

FIG. 26 is a functional diagram illustrating a logic cell utilizable inthe FIG. 18 CLA array.

FIG. 27 illustrates sixteen basic configurations of the FIG. 26 logiccell.

FIG. 28 is a schematic representation of a possible modification to theFIG. 26 logic cell.

FIG. 29 is a logic diagram illustrating an alternate embodiment of alogic cell utilizable in the FIG. 18 CLA array.

FIG. 30 is a logic diagram illustrating a tri-statable output buffercircuit utilizable in the FIG. 18 CLA array.

FIG. 31 is a schematic representation of the sequential configuration ofmultiple CLA arrays of the type shown in FIG. 18.

FIG. 32 is a schematic diagram illustrating a power up sensing circuitutilizable in the FIG. 18 CLA array.

FIG. 33 is a graph illustrating the hysteresis of the FIG. 32 power upsensing circuit.

FIG. 34 is a block diagram illustrating edge core cells and I/O cells inthe FIG. 18 CLA array.

FIG. 35 is a block diagram illustrating express bus I/O cells in theFIG. 18 CLA array.

FIG. 36 is a block diagram illustrating configuration logic for the FIG.18 CLA array.

FIG. 37 is a schematic representation illustrating the loading of aconfiguration file into the internal configuration SRAM within the FIG.18 CLA array.

FIG. 38 is a schematic representation illustrating the bit sequential,internal clock configuration mode of the FIG. 18 CLA array.

FIG. 39 is a schematic representation illustrating the bit sequential,external clock configuration mode of the FIG. 18 CLA array.

FIG. 40 is a schematic representation illustrating the cascadedconfiguration of multiple CLAs of the type shown in FIG. 18.

FIG. 41 is a schematic representation illustrating the parallelconfiguration of multiple CLAs of the type shown in FIG. 18.

FIG. 42 is a schematic representation illustrating the address count-up,internal clock configuration mode of the FIG. 18 CLA array.

FIG. 43 is a schematic representation illustrating the address count-up,external clock configuration mode of the FIG. 18 CLA array.

FIG. 44 is a schematic representation illustrating the byte-sequential,external clock configuration mode of the FIG. 18 CLA array.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 18 shows a configurable logic array 100 comprising a matrix ofindividual programmable logic cells 102. As shown by the "typical" logiccell 102 in FIG. 18, each logic cell 102 receives eight inputs from andprovides eight outputs to its North (N), East (E), South (S) and West(W) neighbors.

These sixteen inputs and outputs are divided into two types, "A" and"B", with an A input, an A output, a B input and a B output for eachneighboring cell. Between cells 102, an A output is always connected toan A input and a B output is always connected to a B input.

As further shown in FIG. 18, the CLA array 100 includes two local bussesL_(W), L_(S) in the x direction and two local buses L_(E), L_(W) in they direction between each row and column of cells 102, respectively, inthe array 100. Thus, each cell 102 has access to four local busses. Thelocal busses allow efficient interconnections between cells 102 that arenot nearest neighbors cells in the same row or column.

Any of these local busses may be active within any given cell 102.However, a cell's connections to local busses must be selected eitheronly as inputs or only as outputs if they are used at all by the cell102, except when used as a bus-to-bus connection or when the FIG. 21alternative scheme, described below, is used. If selected as inputs,then only one of the local busses can be enabled. If selected asoutputs, then a cell 102 can drive up to all four of its accessiblelocal busses.

As shown in FIG. 19, a cell 102 may allow a turn from a local bus L_(W),L_(S) running in the x direction to a local bus L_(E), L_(W) running inthe y direction. This type of connection is useful when twonon-neighboring cells 102 must be connected to one another and the cells102 are not in the same row or the same column. In this case, the cell102 that facilitates the turn cannot use the local busses as an input oran output. If a cell 102 is using its local busses for anything otherthan an input, then the output of the local bus input mux (Lin in FIG.26) is forced to a "1."

FIG. 20 shows the functional implementation of the interface between acell 102 and the local busses.

As shown in FIG. 20, a cell 102 can drive a signal A onto anycombination of its associated local busses, L_(W), L_(S), L_(E) andL_(W) by activating various combinations of the transmission gatescontrolled by signals CL_(W), CL_(S), CL_(E), CL_(W) and CL_(OUT). Acell 102 can receive input from any one of its associated local bussesL_(W), L_(S), L_(E) and L_(W) by activating the transmission gatecontrolled by signal CL_(IN) along with activating one of thetransmission gates controlled by signals CL_(W), CL_(S), CL_(E), andCL_(W). If signal CL_(IN) disables its transmission gate, then p-channelpullup transistor P provides a logic "1" level on signal Lin.

If the transmission gates controlled by signals CL_(OUT) and CL_(IN) areboth disabled, then the local bus interface shown in FIG. 20 canfacilitate a connection from any of its associated local busses to anyor all others. This capability allows turns from a horizontal local busto a vertical local bus.

The cell/bus connection scheme shown in FIG. 20 can be extended toaccommodate a larger number of busses an to allow multiple simultaneousturns between horizontal and vertical busses.

FIG. 20A illustrates an interface scheme that assumes four horizontallocal buses (EW0, EW1, EW2 and EW3) and four vertical local buses (NS0,NS1, NS2 and NS3). For each pair of corresponding buses, e.g. NS0 andEW0, there are three bidirectional pass gates connected in a tree, asillustrated. Each of the eight upper pass gates, i.e. those connecteddirectly to the busses, are controlled by a separate configuration bit.The four lower pass gates, i.e. those connected directly to the cell,may be controlled either by individual bits or, in order to conserveconfiguration bits, by control signals derived from the configurationbits controlled the upper pass gates.

For example, assume that "A" and "B" are the configuration bitscontrolled the upper pass gates associated with NS0 and EW0,respectively. Then either A XOR B or A NAND B can be used to control thecorresponding lower pass gate. Note that, in both cases, the lower passgate is turned off when both upper pass gates are turned on--this is abus turn. Note also that when exactly one of the upper pass gates isturned on, the lower pass gate is also turned on--this is either a writeto the cell. When both upper pass gates are turned off, the state of thelower pass gate is a "don't care".

As in the FIG. 20 scheme, the FIG. 20A scheme uses the same pass gatesfor both reading and writing. In addition, however, it is now possibleto have up to four simultaneous bus turns when the cell is not accessingthe bus, or up to three simultaneous turns when the cell is accessingthe bus.

Alternatively, as shown in FIG. 21, rather than constraining all fourlocal bus connections to all being inputs or all being outputs,configuration memory and multiplexors can be added so that the busconnections can be individually controlled. In this way, one busconnection could be an input and, simultaneously, another bus connectioncould be an output in situations other then bus-to-bus connections. Thiswould reduce the number of cells 102 required for routing in the array100.

As shown in FIG. 22, in addition to the local busses described above,the array 100 includes two express busses X_(W), X_(S) running the xdirection and two express busses X_(E), X_(W) running the y directionbetween each row and column, respectively, of cells 102 in the array100. Each express bus is associated with one local bus. Entry to/from anexpress bus is only possible from/to its associated local bus at theregister.

As shown in FIG. 23A, repeaters R are spaced eight cells 102 apart. Ablock of cells 102 surrounded by repeaters R is referred to as a"superblock". An express bus allows a signal to travel a distance ofeight cells 102 without additional variable loads, giving it the highestspeed possible for the full length of the superblock.

Repeaters R are used to regenerate bus signals and to drive thedifferent bus segments at the superblock interface. A repeater R isshown in FIG. 23B. Under configuration control, the following paths inthe repeater are possible:

    ______________________________________                                        Description:           Path in FIG. 23B                                       ______________________________________                                        Local Bus L1 drives Local Bus L2                                                                     D1-PG3                                                 Local Bus L2 drives Local Bus L1                                                                     D3-PG6                                                 Express Bus X1 drives Express Bus X2                                                                 D2-PG5                                                 Express Bus X2 drives Express Bus X1                                                                 D4-PG8                                                 L1 drives Local Bus L2 & Express Bus X2                                                              D1-PG3 & PG2                                           L2 drives Local Bus L1 & Express Bux X1                                                              D3-PG6 & PG7                                           X1 drives Express Buss X2 & Local Bus L2                                                             D2-PG5 & PG4                                           X2 drives Express Buss X1 & Local Bus L1                                                             D4-PG8- & PG9                                          Local Busses L1 & L2 are single                                                                      PG1                                                    bidirectional bus                                                             (This latter path can be used to make a long busses spanning                  multiple repeaters.)                                                          ______________________________________                                    

Additionally, as shown in FIG. 24, the CLA array 100 can includediagonal interconnections between abutting cells 102. With diagonal cellinterconnection, a substantially smaller number of cells 102 are used bycertain macros for interconnections, thereby improving performance andgate array utilization and increasing the interconnect resources.

As shown in FIG. 24, data flows diagonally from left to right. Each cell102 requires an additional input to the input mux and an additionaloutput to the bottom right. The diagonal interconnected concept can beextended to data flowing diagonally from right to left (top to bottom),left to right (bottom to top) and right to left (bottom to top).

As shown in FIG. 25, the array 100 can include an additional set oflocal vertical buses and an additional set of local horizontal busses.However, instead of these busses being purely vertical and horizontal,as in the case of the local busses discussed above, this second set oflocal busses runs diagonally. Thus, as shown in FIG. 25, one set ofthese busses attaches to the cell's East side and one attaches thecell's South side. In this architecture, every cell 102 is capable ofdriving each of the busses to which it is attached. In this arrangement,each cell 102 in the array 100 can connect more easily to nearby cells102 in a diagonal direction, a very useful feature in compute-intensivealgorithms and in random logic.

Each programmable function of the CLA 100 is controlled by one or moretransistor pass gates, each of which has its pass-or-block statedetermined by the state of a memory bit, either directly or through adecoder. All of these registers are collectively referred to as SRAMConfiguration Data Storage. The advantage of an SRAM (Static RandomAccess Memory), as opposed to a ROM (Read Only Memory), in thisapplication, is that the configuration data can be changed a virtuallyunlimited number of times by simply rewriting the data in the SRAM.

The functional diagram for an embodiment of the logic cell 102 is shownin FIG. 26. It consists of five 4:1 muses, (shown in pass-gate form),cell function logic, and 4 high impedance local bus connectors (alsoshown in pass-gate form) drivers. Three of the 4:1 muxes determine theA, B, and L inputs to be used by the cell function logic. If no input toa mux is selected, then the output of the mux is forced to a logical "1"state. The cell function logic implements the function to be applied tothe A, B and L inputs and supplies the result to the A and B outputmuxes. The four pass gates connecting the cell to the local busses allowthe cell 102 to drive its corresponding local busses or receiverssignals from the busses.

The application of the illustrated technology uses 16 bits of SRAM foreach cell's configuration memory address space to define thefunctionality of the FIG. 26 logic cell 102. Fourteen bits are used forinput and output multiplex control. The remaining two bits are used todetermine the cell's use of its associated local busses. These two bits(BUS0, BUS1), combined with the number of local busses enabled for agiven cell, determine the function of the local busses within the cell,as shown in Table I below. If BUS0 is a "1", then either 1 or 2 of thelocal busses must be selected. Otherwise, any number of local busses maybe selected, within the dictates of Table I.

                  TABLE I                                                         ______________________________________                                                      L's     local bus                                                             en-     function        TRI-STATE                               BUS0  BUS1    abled   within cell                                                                           Li      Control                                 ______________________________________                                        0     0       0       not used                                                                              "1"     "0" (disabled)                          0     0       1-4     output  "1"     "0" (enabled)                           0     1       0       not used                                                                              "1"     "0"                                     0     1       1-4     output  "1"     Bin                                     1     0       1       input   enabled L                                                                             "0"                                     1     0       2       x/y turn                                                                              "1"     "0"                                     1     1       1       mux select                                                                            enabled L                                                                             "0"                                     1     1       2       x/y turn                                                                              "1"     "0"                                     ______________________________________                                    

The function of the cell's control/configuration bits is described inTable II below.

                  TABLE II                                                        ______________________________________                                                    # OF                                                              SIGNALS     BITS     DESCRIPTION                                              ______________________________________                                        CAN, CAS    4        A Input mux selects (zero or one                         CAE, CAW             enabled)                                                 CBN, CBS    4        B Input mux selects (zero or one                         CBE, CBW             enabled)                                                 CLN, CLS    4        L enables (any number, per                               CLE, CLW             Table I)                                                 BUS0, BUS1  2        Determines local bus function                                                 within cell                                              CFUN0, CFUN1                                                                              2        A and B output function select                           ______________________________________                                    

Thus, there are sixteen primary functional configurations of the CLAcell 102, based on the sixteen possible combinations at signals CFUN1,CFUN2, BUS0 and BUS1. FIG. 27 shows the functional diagrams of thesesixteen configurations.

Other applications of this technology may use more (or less) then 16SRAM configuration bits per cell, e.g. to switch the connections ofadditional busses.

FIG. 28 shows a possible modification to the FIG. 26 logic cell 102 thatallows the high impedance control signal to be input over the local busthrough the L mux. Additionally, both the local bus input and the Binput of the cell can be used for control of the high impedance state.This allows the user the flexibility of using either of the inputs forhigh impedance control, thereby saving cells used for wiring. As shownin FIG. 28, the high impedance control signal is provided by the outputof OR gate 104. The L-mux and B-mux outputs, with the high impedanceenable signal, are inputs to the OR gate 104. This facilitates usingeither the local bus inputs (through the L-mux) or the B inputs (throughthe B-mux) as the high impedance control signal.

FIG. 29 shows an alternative embodiment of logic cell 102. The alternatecell utilizes six-state output muxes, giving the user the flexibility ofobtaining the outputs of the XOR, Flip-Flop, NAND and AND functions oneither the A output or B output of the cell. Therefore, the user doesnot have to use an extra cell as a cross-wire for routing to switch theA output to the B output and vice versa.

The alternate cell shown in FIG. 29 requires one extra configuration bitto provide the extra control required for both the A output mux and theB output mux. This extra bit is accommodated by decoding the controlsignals for all of the input muxes, as shown in FIG. 29. If cell spaceis a limitation, then only one input mux must be changed to decodedcontrol (3 lines) signals, with the other two input muxes usingundecoded control signals (4 lines).

FIG. 30 shows an embodiment of a high-performance, high impedance outputbuffer circuit 106, with reduced groundbounce, that is utilizable inconjunction with the CLA array 100. The output buffer circuit 106compensates output buffer slew-rate for process and temperaturevariation to reduce groundbounce with minimal performance impact.

The output buffer 106 is designed to reduce groundbounce by staging theturn on of the upper transistors (P1, P2, P3, . . . Px) and lower outputtransistors (N1, N2, N3, . . . Nx).

The delays between stages are created by transmission gates (TP1, TP2,TP3, TN1, TN2, TN3) in series with capacitors connected at the gates ofthe output transistors. These transmission gates tend to compensate theoutput buffer's slew rate for variations in processing and temperature.Under conditions that would normally cause the output transistors tohave highest current carrying capability and, thus, fastest slew rateand greatest groundbounce, the transmission gates will have lowestimpedance and thus allow the capacitors to which they are connected tohave maximum effect. Under conditions that would normally cause theoutput transistors to have lowest current-carrying capability and, thus,slowest slew rate, the transmission gates will have highest impedanceand thus tend to isolate their corresponding output transistors from thecapacitors to which they are connected. The benefit of this is that, fora given level of groundbounce under fast conditions, the maximum delayof the output buffer under slow conditions can be less than thatpossible using conventional, non-compensating techniques.

FIG. 32 shows an embodiment of a power-up sensing circuit 108 utilizablewith the CLA array 100. The purpose of circuit 108 is to create a resetsignal for the internal logic of the CLA array 100 when the power supplyramps, independent of the ramp rate.

The power-up circuit 108 detects power applied to the CLA device bymonitoring the VCC signal. After VCC reaches the level of two n-channelVts, the PWRERRN signal goes low and stays low until VCC reaches thelevel of two n-channel and two p-channel Vts. The PWRERRN signal canthus be used as a reset signal for the CLA device to ensure that thedevice is in a known state after powers up. When the PWRERRN signal goeshigh, the VCC level necessary to keep PWRERRN high changes to 2n-channel and 1 p-channel Vts. This hysteresis quality, illustrated inFIG. 33, means that power supply spikes down to 2 n-channel and 1p-channel Vt can be tolerated without resetting the chip.

Referring to FIG. 32, the power-up sensing circuit 108 works as follows.N-channel transistors 110, 112, 114 and 116 make up a comparator, withthe gates of transistors 112 and 116 being the comparator inputs.N-channel transistors 118 and 120 have very large gate widths, whileP-channel transistor 122 is very small. This will result in the gate oftransistor 112 being clamped at (2*Vth,n) above ground forVcc>(2*Vtn,n). Both P-channel transistor 124 and P-channel transistor126 are very large and N-channel transistor 128 transistor is verysmall. This would make the input to the transistor 116 gate (2*Vth,p)less than Vcc, for Vcc>(2*Vtn,P). As Vcc ramps up, while the Vcc to GNDvoltage is less than (2*Vth,p+2*Vth,n) the transistor 112 gate will beat a higher potential than the transistor 116 gate. This will result inthe comparator output (m) providing a logic "1" level to the input ofinverter 130 input causing the power up signal to be at a logic "0"level. Once the Vcc to GND potential exceeds (2*Vth,n+2*Vth,p) thetransistor 112 gate will be lower than the transistor 16 gate. This willcause the (m) node to be at a logic "0" level, and the power up outputto be at a logic "1" level. This indicates that the power is at asufficient level to support proper device operation. Hysteresis isprovided by P-channel transistor 132. When the gate of transistor 132 ishigh, transistor 132 is disabled, and the circuit operates as describedabove. After node (m) goes low, the gate of transistor 132 will bepulled to ground by inverter 134. Thus, transistor 132 will effectivelyshort the source of transistor 126 to its drain, thereby lowering theVcc to GND voltage needed to cause node (m) to be at a logic "1" levelto (2*Vtn,P). Therefore, the Vcc to GND differential will have to fallto (1(Vth,p) plus (2*Vth,n) before the power up signal provided byinverter 136 will go low.

In accordance with another aspect of the CLA device 100 architecture,I/O cell pins are provided that are connected directly to the array'sexpress busses in addition to the edge core cells.

As stated above, the architecture of the CLA device 100 comprises aregular array of logic cells 102. I/O pins in I/O cells are attacheduniformly around the periphery of the array. An I/O cell is connected totwo adjacent edge core cells 102 of the array.

FIG. 34 shows an example of pin Pw23 in an I/O cell connected to twocore cells 102 on the west edge of the array 100. The input buffer Cinof the Pw23 I/O cell is connected to an A input of an edge core cell viawire Aw12. The output buffer Cout is connected to an A output of anadjacent edge core cell via wire Aw13. Placing of the output buffer Coutin the high impedance state can be controlled by configuration (alwaysenabled or disabled) or by signals on a horizontal or vertical buss, Ls3or Lw1 respectively.

Express busses running horizontally and vertically are connected to A orB inputs and outputs of edge core cells (e.g. express buses Es1, En1,Es2, En2, Es3 and En3 in FIG. 34).

In a modified architecture, a new type of I/O cell is added. These newexpress bus I/O cells connect directly to the express busses instead ofbeing connected to a core cell. FIG. 35 shows an example of an expressbus I/O cell Pw12 adjacent to I/O cell Pw23.

The express bus I/O cells make only minor modifications in thearchitecture of the CLA device 100. As in the regular I/O cells, highimpedance is controlled at configuration or by the horizontal andvertical local busses Lw1 and Ls2, respectively. Unlike the regular I/Ocell, however, input buffer Cin and output buffer Cout are connecteddirectly to express busses En1 and Es2, respectively, and the expressbus links that previously went to the core cells are disconnected fromthe express busses; for examples, express bus Es2 is not connected to Aoutput A12 and express bus En1 is not connected to A input Aw11.

The addition of the express bus I/O cells allows direct access toexpress busses, thus improving access to interior regions of the array100 and improving its cross-point switch capabilities.

FIG. 36 shows a block diagram of the configuration logic for the CLAarray 100.

The device pins required for configuration of the CLA array 100 are asfollows:

The dedicated pins are:

/Con Configuration Request Pin (Open collector I/O). This pin is pulledlow along with /Cs by the user to initiate configuration. Once thedevice has begun configuration, it will drive /Con low untilconfiguration is complete. The device will also pull /Con low during thepower-up and reset sequences. The chip will auto-configure in modes 4and 5 (as shown in Table III).

/Cs Chip Select (Input). Must be pulled low with /Con to initiateconfiguration or reset.

Cclk Configuration Clock (Input/output). This signal is the byte clockin Address modes, and the bit clock in bit-sequential modes. In thebyte-sequential mode, this pin is used as an active low write strobe. Indirect-Address mode, this is an active low data strobe. Cclk is not usedduring configuration in modes 4 and 5 with a frequency between 1 and 1.5MHz. In all other modes, Cclk is an input, with a maximum frequency of16 MHz. Note that cascaded programming will not work in byte-sequentialor Address modes with as Cclk of over 1 MHz.

The Mode pins M2, M1, M0 (input) are used to select the configurationmode, as described in Table III.

                  TABLE III                                                       ______________________________________                                        M2   M1      M0     Description of Modes                                      ______________________________________                                        0    0       0      Configuration Reset                                       0    0       1      Address, Count up, external CCLK                          0    1       0      Address, Count down, external CCLK                        0    1       1      Bit-Sequential, external CCLK                             1    0       0      Bit-Sequential, internal CCLK                             1    0       1      Address, Count up, internal CCLK                          1    1       0      Byte-Sequential, external CCLK as write                                       strobe                                                    1    1       1      Direct Addressing, external CCLK as data                                      strobe                                                    ______________________________________                                    

The dual-purpose pins are:

D0 Data pin (Input/Output). This pin is used as serial data input pin,and as the LSB in byte-sequential, direct addressing and Address modes.Used as an I/O only in direct address mode.

D1-7 Data pins (Input/Output). These pins are used as data input pins inbyte-sequential and Address modes and as I/O only in direct addressmode.

A0-A16 Address pins (Input/Output). 17 bits of address are used asoutputs during Address modes for accessing external memory. 13 bits arealso used as internal address inputs for the configuration RAM in directaddress mode.

/Cen Chip enable (Output). This signal is driven low by the deviceduring configuration in byte-sequential and Address modes. It can bedisabled by setting configuration register bit B2. It is used for theOutput Enable (OE) and Chip Enable (CE) of parallel EPROMs.

/Check Enables Check configuration (Input). This pin enables checking ofthe configuration RAM against data on input pins. If this pin isenabled, then writing configuration data is disabled. This pin isdisabled during the first configuration after power-up or reset, andwhenever configuration register bit B3 is set. In direct access mode,this pin selects whether data is being written to or read from theconfiguration RAM.

/Err Error (Output). This output is driven low if there is aconfiguration error, a configuration RAM addressing error, or anincorrect preamble or postamble at the end of a block of configurationdata. It also signals the result of the configuration check, selectedwhen /Check is low. This output is disabled when configuration registerbit B3 is set.

Dout Data out (Output). This pin provides the data output to another CLAdevice during cascaded programming. It can be disabled by settingconfiguration register bit B2.

Clkout Clock out (Output). This pin provides the clock output to anotherCLAY during cascaded programming. It can be disabled by settingconfiguration register bit B2.

Testclk Test clock (Input). This pin overrides the internal oscillatorafter a certain reserved configuration bit is set to logical "1". Thisfeature is used for internal testing purposes.

The CLA array 100 can be in either an operational state or in aconfiguration state. After initial configuration, the device moves intothe operational state. It can be pulled back into the configurationstate by insertion of the "/Con" and "/Cs" inputs.

The configuration file, in a cascaded programming environment, is shownin Table IV below. The first CLA device in the cascade receives thePreamble. This is followed by the contents of the configurationregister, an optional external memory address, and the number of windowsin the first CLA device that need to be programmed. The start/stopaddresses for each window and the configuration data follow. Theconfiguration data (including header) for the cascaded devices areappended to the file. If the configuration register specifies that thedevice needs to load an external memory address, then this address isloaded every time it encounters that field. When the master has finishedconfiguring itself, it looks for a preamble or postamble. If it finds apostamble, then configuration is complete. If it receives a preamble,then it passes on the data and clock to configure the next CLA device inthe cascade.

                  TABLE IV                                                        ______________________________________                                        Preamble                  (1 byte)                                            Config reg contents for first device                                                                    (1 byte)                                            External Memory Address   (3 bytes)                                           Number of windows to be programmed                                                                      (1 byte)                                            Reserved Byte             (1 byte)                                            Start address of window number 1                                                                        (2 bytes)                                           End address of window number 1                                                                          (2 bytes)                                           Bytes of data for window number 1                                                                       (1 byte each)                                       Start address of window number n                                                                        (2 bytes)                                           End address of window number n                                                                          (2 bytes)                                           Bytes of data for window number n                                                                       (1 byte each)                                       Preamble                  (1 byte)                                            Config reg contents for cascaded device                                                                 (1 byte)                                            External Memory Address (for first device)                                                              (3 bytes)                                           Reserved Byte             (1 byte)                                            Number of windows to be programmed                                                                      (1 byte)                                            Postamble                 (1 byte)                                            ______________________________________                                    

The first CLA device loads itself until it exhausts the number ofwindows it has to configure. Any data after this and within theconfiguration file is used for cascaded devices. At the end ofconfiguration, the external memory address counter in the first deviceis either reset or stored at the current value depending on the state ofbit 0 in the configuration register. The preamble is "10110010" and thepostamble is "01001101". Serial data is transmitted LSB first.

The clock description for each mode is shown in Table V below.

                  TABLE V                                                         ______________________________________                                        M2      M1     M0        Clkout  CSM   CCLK                                   ______________________________________                                        0       0      0         NA      NA    NA                                     0       0      1         osc     cclk  input                                  0       1      1         cclk    cclk  input                                  1       0      0         cclk    cclk  osc/8                                  1       0      1         osc     cclk  osc/8                                  1       1      0         osc     /wr   /wr                                    1       1      1         NA      NA    /DS                                    ______________________________________                                    

Osc is the internal oscillator which runs between 8 and 12 MHz.

/WR is the Cclk input used as a write strobe.

/DS is the Cclk input used as a data strobe.

In modes 1, 2, and 6, data is output on the Dout pin along with theclock on the clkout pin. The configuration scheme allows the user toprovide a Cclk at up to 16 MHz for these modes. However, for cascadedprogramming and other applications where Clkout and Dout are required,the speed of Cclk must be less than 1 MHz in these modes.

To specify the desired application function, the user must load theinternal SRAM which the CLA device uses to store configurationinformation. The user does not need to generate the SRAM bit pattern;this is done for the user by the Configurable Logic Array SoftwareSystem.

The user must also determine the method by which the configuration RAMis loaded. Many factors, including board area, configuration speed, andthe number of designs concurrently implemented in a device can influencethe user's final choice.

The CLA provides seven configuration modes:

Mode 0: Configuration Reset

Mode 1: Address Count-up, External CCLK

Mode 2: Address Count-down, External CCLK

Mode 3: Bit-sequential, External CCLK

Mode 4: Bit-sequential, Internal CCLK

Mode 5: Address Count-up, Internal CCLK

Mode 6: Byte-sequential, External CCLK

Mode 7: Direct Addressing, External CCLK

Upon power-up, the CLA goes through a boot or initialization sequence.This sequence initializes all core cells, repeaters, I/O logic, clockdistribution logic, and open collector controls, as well as theconfiguration register and external memory address counter (discussedbelow).

Core cells become flip-flops with A_(N) and B_(N) inputs.

All bus drivers are switched off.

All repeaters are open and all bus segments are high impedance.

I/Os are set as TTL inputs only, with the pull-up on.

Column clocks are set to "0".

All open collector controls are set for full CMOS drive.

Each of the bits in he configuration register is reset.

During the initialization sequence, the CLA device 100 drives the /CONpin low. Since power-up initialization uses an internal clock fortiming, no external clock source is required. Once initialization iscomplete, /CON, which is an open collector output, is released; it mustbe pulled high by an external pull-up resistor.

After power-up initialization is complete, the CLA device 100 is readyto accept the user's configuration. After /CON has been released for aminimum period of time, the user can initiate the configuration cycle bydriving /CS and /CON low (in some modes this can take placeautomatically). The configuration mode is determined by the values onthe M0, M1, and M2 pins, as described above. Once the first bytes of theconfiguration have been loaded, the CLA device 100 takes over driving/CON low, the values on the M0, M1, and M2 pins are ignored, and /CS canbe released high. The CLA device 100 will release /CON only after thecomplete configuration file has been read. It will remain in theconfiguration state until both /CON and /CS are released.

The CCLK pin should be driven with the configuration clock (in ExternalCCLK Modes) and the M0, M1, and M2 pins held constant throughout thereboot and configuration sequences.

The user can reconfigure the CLA device 100 at any time by asserting/CON and /CS, as outlined above. The CLA device must be allowed to moveinto the operational state (/CON and /CS high) between configurations.Note that those pins not required for configuration remain operationalthroughout a configuration sequence allowing partial reconfiguration ofan operational device.

Details of each configuration mode are described below.

The configuration file which is stored in an external memory device isused to load the user's configuration into the internal configurationSRAM within the CLA, as shown in FIG. 38. This file has a similarformat, shown in Table VI, regardless of the configuration mode(sequential, or Address).

                  TABLE VI                                                        ______________________________________                                        Configuration File Formats                                                    ______________________________________                                        Single CLA          Cascaded CLAs                                             Preamble            Preamble                                                  Header              Header                                                    [Window 1]          [Window 1]                                                [Window 2]          [Window 2]                                                [Window 3]          [Window 3]                                                [Window n]          [Window n]                                                Postamble           Preamble                                                  Header 2                                                                                          [Window 1]                                                                    [Window 2]                                                                    [Window 3]                                                                    [Window n]                                                                    Preamble                                                                      Preamble                                                                      Header n                                                                      [Window 1]                                                                    [Window 2]                                                                    [Window 3]                                                                    [Window n]                                                                    Postamble                                                 ______________________________________                                    

The preamble is a fixed data byte used to synchronize the serial bitstream in sequential modes, and to signal the start of the configurationfile in all modes.

The header is a five byte field which includes configuration registerdata, the external memory address for Address modes, and a counter forthe number of CLA data windows to be programmed.

The configuration register includes five bits used to control variousconfiguration sequence parameters. Information regarding these five bitsfollows. ##STR1## wherein: B0 This bit determines whether the externalmemory address in Address modes is reset after each configurationsequence (default), or if it retains its last value. This allows theuser to store multiple designs as sequential configuration files.Otherwise, the subsequent configuration sequences will load theconfiguration file from the same initial address (00000 in modes 1 and5, 1FFFF in mode 2).

B1 This bit determines whether the external memory address in the headfield(s) will be ignored (default) or loaded into the CLA's externalmemory address counter. This allows the user to store configurationfiles as a continuous stream or as a pointer-based linked list.

B2 This bit disables the /CEN, DATAOUT, and CLKOUT functions of thesemultiplexed configuration pins. This is useful if a minimum pin countconfiguration circuit is desired.

B3 This bit disables the /ERR and /CHECK pins. This is useful both fordesign security and minimum pin-count configurations.

B4 This bit prevents configuration data from being written into the CLAduring subsequent configuration sequences. The only way to reset thisbit is by rebooting the device.

The external memory address is used to set the external memory addresscounter of the CLA device 100 in the Address modes. This counterincrements on every configuration clock in order to drive the address ofan external memory device to generate a parallel data stream. Thecounter counts up in Modes 1 and 5, and down in Mode 2. The newprogrammed value will be output after each header has been read,according to the configuration bit settings. Note that the externaladdress is for use by external memory. It has no relationship with theinternal configuration SRAM within the CLA device 100. Configurationdata is read into the CLA device 100 in a stream format.

Another header byte loads the number of windows counter. Configurationdata windows make it possible to configure or reconfigure one or moresub-sections of the device. It is possible to load the entire CLA arrayusing a single window. Multiple windows allow the user to jump oversections of the CLA array, thus saving configuration time and memory forlightly used arrays.

Data windows also support the creation of dynamic CLA designs, as smallsections of the array can be reconfigured regularly as part of thedesign's functionality. The optimum set of configuration data windowsare generated automatically by the CLA's development system. Only thesection of the array selected by the user for reconfiguration will beprogrammed. There can be a maximum of 255 windows per CLA device 100. If0 windows are specified, then the array's configuration will not bemodified. This is useful if multiple CLA device 100 are being configuredsimultaneously.

Each configuration data window consists of an internal array startaddress, an internal array end address, and the sequential data requiredto fill the segment of the array defined by the two addresses.Internally, the array is represented as a circular address space. Theconfiguration data stream sequence is divided such that cell types aregrouped together in the following order:

Core Cell Configuration Data

Bus Repeater Cell Data

I/O and Clock Cell Data

Open Collector Control Data

If a single CLA device 100 is being configured, then the configurationdata windows are followed by a postamble. This is a fixed data bytewhich signals the end of the configuration file. If multiple CLA devices100 are being cascaded, however, another preamble byte will appear atthis point in the configuration file. This preamble will be followed byanother header and a new set of configuration data windows.Theoretically, any number of CLA devices 100 can be programmed in thisfashion. In actual practice, however, it is recommended that not morethan 8 CLA devices 100 be linked in this cascaded fashion, due topotential clock skew problems.

Configuration reset is not a true configuration mode. It is used tostart the boot sequence. Enabling this mode is equivalent to turningpower to the device off and on again, except that the state of thecore's user-accessible flip-flops is saved. This mode is enabled byasserting /CS, /CON, M0, M1, and M2 low for a minimum period of time andthen returning them to the desired mode. Once the reboot process isstarted, it overrides any other configuration sequence that may berunning and cannot be stopped.

The remaining configuration modes load all or some of the CLA device'sinternal configuration SRAM.

Bit-sequential, internal CCLK mode 4 is the simplest of configurationmodes, as it requires the fewest pins and the fewest externalcomponents. For a single CLA device, only one dual-function pin, D0, isneeded for data received from a serial EPROM. The other dual-functionpins, /CEN, /ERR, /CHECK, DATAOUT, and CLKOUT, are all optional.Assuming the /CS and mode pins (M0, M1 and M2) are fixed, the onlyactive pins are /CON, CCLK, and D0. Because most serial EPROMs come in8-pin DIP packages, little board space is required for thisconfiguration mode, as shown in FIG. 38.

During the power-up boot sequence, /CON is asserted low by the CLAdevice. Once initialization is complete, /CON is released long enough toreset a serial EPROM. If the mode pins are set to mode 4 before releaseof /CON, the CLA will then begin autoconfiguration. It reasserts /CONlow and an internal oscillator toggles CCLK. This causes the serialEPROM to generate a stream of data which configures the CLA device 100.One bit of configuration data is loaded from the D0 pin on each risingedge of CCLK until configuration is complete. The CLA device 100 willthen release /CON indicating that the device 100 is ready for use.

Configuration time will vary depending on the speed of the internaloscillator, but the maximum configuration time for a complete array isabout 80 milliseconds.

Bit-sequential, External CCLK (Mode 3) is very much like Mode 4, above,with two exceptions: the user must supply a configuration clock to theCCLK pin and the user most drive /CON low to start configuration. Mode 3will not automatically generate a /CON signal after the power-up bootsequence. During configuration, only one dual-function pin, D0, isrequired. The pins /CEN, /ERR, /CHECK, DATAOUT, and CLKOUT are optional.The only active pins are /CON, CCLK, and D0, as shown in FIG. 39.

Mode 3 can be used for the cascaded configuration of multiple CLAdevices 100, as shown in FIG. 40. The first device 100 in a chain canuse any configuration mode. If the first device 100 receives aconfiguration file containing another preamble instead of a postamble,then the remaining configuration data will be ignored by the firstdevice 100 and passed on through its DATAOUT and CLKOUT pins to the nextdevice. The DATAOUT pin of an upstream device 100 goes to D0 of thedownstream device 100, and the upstream CLKOUT pin connects to thedownstream CCLK. In Mode 3, the CLKOUT signal is derived directly fromthe CCLK Input. The /CON pins of each device 100 in the cascade can betied together to create a single "configuration complete" signal.

It is also possible for an external processor to configure multiple Mode3 CLA devices 100 in parallel by assigning a unique bit of its data pathto the D0 of each device 100, and tying the CCLK inputs of the devices100 together as a write strobe, as shown in FIG. 41.

One advantage that the Mode 3 has over Mode 4 is that, depending on theaccuracy of the user-supplied clock, the time required to configure thedevice 100 can be determined precisely. Also, because the user cansupply a faster maximum clock rate than the typical internally-generatedclock range, Mode 3 can be a faster configuration method. As long asdata set-up and hold requirements are satisfied, the CCLK pulses canhave arbitrary periods. Such a clock is required when using asynchronouscommunication ports or UARTs to configure the device 100 instead of aserial EPROM. It is necessary, however, to allow sufficient precedingand trailing clock pulses with respect to /CON going low CCLK is to bestopped entirely between configurations.

Count-up Address, Internal CCLK (Mode 5) mode requires the same numberof parts as Mode 4, but uses more dual-function I/O pins during theconfiguration sequence. Because serial EPROMs are not currentlyavailable in sizes large enough of all multiple-device designs, theincreased memory of a parallel EPROM is sometimes necessary. With thestandard parallel EPROM, this configuration mode uses the C0-D7 datapins, the A0-A16 address pins, /CEN, and the fixed function pins, asshown in FIG. 42.

/CHECK, DATAOUT, and CLKOUT pins are optional in this mode.

Mode 5 supports auto-configuration. If the mode pins are setappropriately before the release of /CON during the power-up bootsequence. After a brief period, the CLA device reasserts /CON low, andthe internal oscillator begins to toggle CCLK. This causes the CLAdevice 100 to generate addresses, beginning at 0X00000 to read theconfiguration file from the parallel EPROM. The external memory addressis incremented and one byte of configuration data is loaded from theD0-D7 pins on each rising edge of CCLK until configuration is complete.The CLA device 100 will then release /CON, indicating that the device100 is ready for use.

Thirteen address bits are required to fully program a single CLA device100; the extra addresses allow multiple device configuration andreconfiguration, as well as the ability to share a large memory spacewith other components of a system. If cascading it necessary, theparallel input data is automatically converted to a serial data outputstream on the DATAOUT and CLKOUT pins. Configuration time will varydepending on the speed of the internal oscillator, but the maximumconfiguration time per array in this mode is about 10 milliseconds.

The Count-up Address, External CCLK (Mode 1) mode is very much like Mode5, above, with two exceptions: the user must supply as configurationclock to the CCLK pin and the user must always drive /CON low to startconfiguration. Mode 1 will not automatically generate a /CON signalafter the power-up boot sequence. This configuration mode uses the D0-D7data pins, the A0-A16 address pins /CEN and the fixed function pins, asshown in FIG. 43.

/CHECK, DATAOUT, and CLKOUT pins remain operational in this mode.

In Mode 2, the user can supply the maximum clock rate in order tocomplete configuration of a single device in under 1 millisecond. Theuse of cascading however, limits the parallel data rate to 800 KHz,since the internal clock is used to drive the CLKOUT pin. As in Mode 3,the CCLK signal can be synchronous or asynchronous.

The Count-Down Address, External CCLK (Mode 2) is identical to Mode 1,above, except that the DMA address counter starts at 1FFFF instead of00000, and counts down instead of up. The two modes are included becausea typical microprocessor uses the highest or lowest address to load itsown reboot address vector. If the CLA device 100 is sharing a largeEPROM with a microprocessor, it must start from the opposite end of theEPROM address map so that it does not interfere with the microprocessor,and vice versa.

The Byte-sequential, External CCLK (Mode 6) mode is similar to Mode 3,except that data is loaded in 8-bit words to decrease load time. Thismode uses fewer dual-function pins than the does the Address modebecause the CLA device 100 does not generate an address instead, thenext byte in the data stream is assumed to be present on the rising edgeof CCLK. During configuration, D0-D7 are the only dual-function pinsrequired, as shown in FIG. 44. The pins /ERR, /CHECK, DATAOUT, andCLKOUT are optional. The CCLK requirements are the same as for Mode 1.

Intended to be used as the parallel port of a microprocessor, this modemay be best for a smart system in which the user intends to reconfigurethe CLA device 100 as a regular part of system operation. Multiple CLAdevices 100 can be configured by tying all the data busses together, aswell as the /CON pins. The /CS pins can then be used to selectindividual devices for configuration. Alternatively, multiple CLAdevices 100 can be configured in parallel by assigning each byte of a32-bit processor's data path to a unique CLA device 100, and tying theCCLK inputs of the CLA devices 100 together as a common write strobe, asshown in FIG. 31. It is also possible to program the first device 100 inMode 6, and cascade all downstream devices 100 in Mode 3 as outlinedpreviously.

It should be understood that various alternatives to the embodiment ofthe invention described herein may be employed in practicing theinvention. For example, although the inventive concepts are describedabove in the context of reconfigurable logic, these concepts are alsoapplicable to one-time programmable logic. It is intended that thefollowing claims define the scope of the invention and that methods andapparatus within the scope of these claims and their equivalents becovered thereby.

What is claimed is:
 1. In a configurable logic array that includes aplurality of individually configurable logic cells arranged in agenerally rectangular matrix that includes a plurality of horizontalrows of logic cells and a plurality of vertical rows of logic cells, thearray further including at least one horizontally aligned express busrunning between adjacent rows of logic cells, said logic cells in saidadjacent rows being connectable thereto, and at least one verticallyaligned express bus running between adjacent columns of logic cells,said logic cells in said adjacent columns being connectable thereto, thearray further including a plurality of logic cells I/O pins located atthe periphery of the matrix and connectable to the logic cells in therows and columns at the periphery of the matrix, the improvementcomprising a plurality of express bus I/O pins directly connectable tothe express busses.